High surface area cathode assembly, system including the assembly, and method of using same

ABSTRACT

A cathode assembly, a system including the cathode assembly, and method of using the assembly and system are disclosed. The cathode assembly includes high surface area material to allow efficient recovery of metal at reduced current densities at the cathode, which allows increased rates of metal recovery to be obtained, while maintaining desired properties of the electrowon metal.

FIELD OF INVENTION

The present invention generally relates to cathode assemblies for use in electrolytic metal recovery processes. More particularly, the invention relates to high surface area cathode assemblies for electrolytic recovery of metal, to systems including the cathode assemblies, and to methods of using the cathode assemblies and systems.

BACKGROUND OF THE INVENTION

Electrowinning is often used in hydrometallurgical processing of ore to recover metal, such as copper, silver, platinum group metals, molybdenum, zinc, nickel, cobalt, uranium, rhenium, rare earth metals, combinations thereof, and the like from ore. The recovery of metal from ore often includes exposing the ore to a leaching process (e.g., atmospheric leaching, pressure leaching, agitation leaching, heap leaching, stockpile leaching, thin-layer leaching, vat leaching, or the like) to obtain a pregnant leach solution (PLS) including desired metal ions, optionally purifying and concentrating the pregnant leach solution, using, e.g., a solvent extraction process, and then recovering the metal using the electrowinning process.

A typical electrolytic cell for electrowinning includes an anode assembly, a cathode assembly that is spaced apart from the anode assembly, an electrolyte solution, and a tank to contain the electrolyte solution. An active area of the cathode assembly, which is generally the conductive portion of the cathode assembly immersed in the electrolyte solution, often comprises a solid metal plate.

In an electrowinning process, metal is recovered from the electrolyte solution by applying a bias across the cathode assembly and the anode assembly sufficient to cause the metal ions in solution to migrate towards and reduce onto an active area of the cathode assembly—e.g., a portion of the metal plate.

In a typical electrolytic cell for electrowinning, a rate of metal recovery from electrowinning is a function of, among other things, current density at the cathode, which is defined as the current flowing through the electrolytic cell divided by the active area of the cathode. Over a certain current density, known as limiting current density, reactions, other than metal deposition and which are generally undesirable, begin to occur. In addition, as current densities are increased, a quality of the metal deposited onto the cathode may decrease, even when the current density is maintained below the limiting current density. For example, the granularity of the metal and/or amount of impurities included in the deposited metal generally increases as the current density increases. Thus, although higher current densities may be desirable to achieve higher plating rates, the higher current densities may be problematic.

Another difficulty with traditional electrowinning is metal recovery from low quality liquid streams, such as acid mine drainage, low grade PLS, bleed streams, and remediation streams. Traditional cathode assemblies may require high current densities to extract metal from low quality streams, which may result in higher energy costs and increased impurities in the deposited metal.

Additionally, traditional electrowinning cell systems are typically large, industrial scale apparatus which operate in permanent locations. Many low grade metal supplies, such as acid mine drainage and remediation streams, may therefore require collection and transport to an industrial electrowinning facility. In certain circumstances, removal and transport of metal bearing liquid may create logistic difficulties, and may lead to increased costs and time associated with recovering the metal.

Accordingly, improved apparatus and methods for plating metal at higher effective rates at lower current densities, for recovering metal value from low grade supplies, and for recovering metal at or near the source of the low grade supplies are desired.

SUMMARY OF THE INVENTION

The present invention generally relates to a cathode assembly for use in an electrolytic metal recovery process, to a system including the cathode assembly and to methods of using the cathode assembly and system. While the ways in which the present invention addresses the various drawbacks of the prior art are discussed in greater detail below, in general, the cathode assembly, system, and method in accordance with various exemplary embodiments of the invention provide a cathode assembly having a high cathode active area, which allows for increased efficiency of the electrowinning system and/or increased metal recovery rates while maintaining recovered metal purity.

In accordance with various exemplary embodiments, a cathode assembly includes a hanger bar and high surface area material coupled to the hanger bar. The cathode assembly may include a connecting element to join the high-surface area material to the hanger bar.

In accordance with additional exemplary embodiments, a cathode assembly includes a hanger bar, high surface area material, and at least one conductor element coupled to a high surface area material and the hanger bar. In accordance with various aspects of these embodiments, the cathode assembly includes a flow-through container, formed of, for example, non-conductive material, about at least a portion of the high surface area material. In accordance with further aspects, the container includes voids, such that the container has an open area of about 20% to about 80%. In accordance with yet additional aspects of these embodiments, the cathode assembly includes at least one connecting element coupled to the container and the hanger bar.

In accordance with additional embodiments of the invention, a system for electrolytic recovery of metal includes a tank, an electrolyte solution comprising metal ions within the tank, an anode assembly, and a cathode assembly, having high surface area material, a hanger bar, and optionally a conductive element coupled to the hanger bar and the high surface area material. In accordance with various exemplary aspects of these embodiments, the electrolyte solution comprises pregnant leach solution, and in accordance with particular aspects, the leach solution has not been treated with a solvent extraction process. In accordance with further aspects, the cathode assembly includes a flow-through container, formed of, for example, non-conductive material, to contain the high-surface area material, coupled to the hanger bar, using, e.g., one or more connecting elements. In accordance with further aspects, the container includes voids, such that the container has an open area of about 20% to about 80%. And, in accordance with yet additional embodiments, the system is portable, such that it can be brought to and used at locations at or near the source of a metal-containing solution.

In accordance with yet additional embodiments of the invention, a method for recovering metal includes the steps of providing a tank, providing an electrolyte solution in the tank, providing an anode assembly, such that an active area of the anode assembly is in contact with the electrolyte solution, and providing a cathode assembly, wherein the cathode assembly includes a hanger bar, high surface area material, and optionally a conductor element coupled to a high surface area material and the hanger bar. In accordance with various aspects of these embodiments, the cathode assembly includes a flow-through container to contain the high-surface area material. In accordance with further aspects, the container includes voids, such that the container has an open area of about 20% to about 80%. In accordance with yet additional aspects of these embodiments, the cathode assembly includes at least one connecting element coupled to the container and the hanger bar. In accordance with yet additional aspects, the electrolyte includes a metal supply such as a pregnant leach solution. In accordance with further embodiments, the method further comprises the steps of selecting a site having a low grade metal supply and placing an electrowinning system near the low grade metal supply. As discussed in more detail below, electrolytic recovery of metal in accordance with these embodiments produces relatively high-quality metal at greater efficiency, compared to typical techniques for recovering metal.

These and other features and advantages of the present invention will become apparent upon a reading of the following detailed description when taken in conjunction with the drawing figures, wherein there is shown and described various illustrative embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein:

FIG. 1 illustrates a front-view of a cathode assembly in accordance with various exemplary embodiments of the invention;

FIG. 2 and FIG. 3 illustrate cathode assemblies in accordance with additional embodiments of the invention;

FIG. 4 illustrates an electrolytic metal recovery system in accordance with exemplary embodiments of the invention; and

FIG. 5 illustrates a method of electrowinning metal in accordance with exemplary embodiments of the invention.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of illustrated embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The description of exemplary embodiments of the present invention provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the invention disclosed herein. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features. While these embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, it should be understood that other embodiments may be realized and that mechanical and other changes may be made without departing from the spirit and scope of the present disclosure.

As set forth in more detail below, for a given metal recovery rate, the cathode assembly, system including the assembly, and method of using the assembly and system, in accordance with various embodiments of the invention, provide increased efficiency and better electowon metal quality compared to conventional assemblies, systems, and methods.

The cathode assembly, system, and method described herein can be used in a variety of applications, such as electrowinning various metals. The cathode assembly and system can be used to recover, for example, metals such as copper, gold, silver, zinc, platinum group metals, nickel, chromium, cobalt, manganese, molybdenum, rhenium, uranium, rare earth metals, alkali metals, alkaline metals, and the like. For example, the assembly and system of the present invention may be used in connection with recovery of copper from hydrometallurgical processing of copper sulfide ores and/or copper oxide ores. By way of particular example, the assembly, system, and method can be used to recover copper from a pregnant leach solution containing copper ions—without concentrating the leach solution (e.g., via treating the pregnant leach solution with a solvent extraction process).

FIG. 1 illustrates a front view of a cathode assembly 100 in accordance with various exemplary embodiments of the present invention. Assembly 100 includes a hanger bar 102, high surface area material 104, and connecting element 112.

High surface area material 104 may be formed of a variety of materials in a variety of configurations. In general, high surface area material 104 has a surface area to volume ratio of about 0.05 to about 10 ft²/in³. In various exemplary embodiments, the surface area to volume ratio may be in the range of about 0.1 to about 5 ft²/in³. In a preferred embodiment, the surface area to volume ratio may be in the range of about 0.1 to about 1 ft²/in³. To obtain the relatively high surface area per volume, material 104 may be configured as, for example, metal hair, metal wool, metal fabric, metal foam (open or closed cell), conductive polymers, or the like. As used herein, metal hair refers to spun metal wire having a diameter of about 0.001 to about 0.01 inches, and metal foam refers to an open cellular structure having a large volume fraction of open pores. The percent open volume of the metal foam is about 20% to 80% open. Material 104 may also include surface treatments or coatings to facilitate recovery of metal plated onto material 104.

Exemplary materials suitable for material 104 include copper, copper alloy, copper aluminum alloys, stainless steel, titanium, aluminum, combinations thereof, or other suitably conductive material. By way of one example, material 104 includes copper wire hair having a diameter of about 0.005 inches and a surface area to volume ratio of about 0.5 ft²/in³.

Hanger bar 102 is designed to form electrical contact between a portion of a metal recovery system, discussed in more detail below, and high surface area material 104. Hanger bar 102 may be formed of a variety of materials such as copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, combinations thereof, or other suitably conductive material. By way of particular example, hanger bar 102 is formed of copper.

Connecting element 112 is designed to physically connect and/or electrically couple high surface area material 104 to hanger bar 102. As illustrated in FIG. 1, high surface area 104 is held in physical contact with and electrically coupled to hanger bar 102 by connecting element 112. Connecting element 112 may comprise exemplary materials such as copper, copper alloy, copper aluminum alloys, stainless steel, titanium, aluminum, combinations thereof, or other suitably conductive material. Further, connecting element 112 may be physically connected to high surface area material using additional means, such as bolts 130. However, any means by which connecting element 112 may use to maintain physical connection to high surface area material 104 is in accordance with the present disclosure.

FIG. 2 illustrates a cathode assembly 200 in accordance with various exemplary embodiments of the present invention. Assembly 200 includes a hanger bar 202, high surface area material 104, connecting element 212, a flow-through container 210, and optionally, at least one conductive element 208.

Flow-through container 210 is configured to maintain high surface area material 104 within a desired area and to allow electrolyte to flow through the active area of cathode assembly 200. In accordance with exemplary embodiments of the invention, container 210 may be configured in the form of a bag, a cage (e.g., a wire cage), a woven wire container, an open honey-comb configuration, or, as illustrated, container 210 may be configured as an open-top box having openings through the container walls. In accordance with various aspects, container 210 includes holes, such that container 210 has an open area of about 20% to about 80%. As illustrated in FIG. 2, holes 216 provide open area which allows electrolyte to flow through the active area of cathode assembly 200.

Container 210 may be an integral unit or, as illustrated, may be formed of multiple sections, e.g., walls 220-226 and a bottom 228. When formed of multiple sections, the sections may be coupled together using, for example, adhesive or removable fasteners, such as nuts and bolts, and the like.

Container 210 may be formed of a variety of materials. In accordance with exemplary embodiments of the invention, container walls 220-226 and container bottom 228 are formed of non-conductive material, such as polyethylene, polystyrene, polyvinyl chloride and/or a polytetrafluoroethylene (PTFE). However, in accordance with alternative examples of the invention, container 210 may be formed of conductive material, such as copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, combinations thereof, or other suitably conductive material.

Connecting element 212 is designed to physically couple hangar bar 202 and container 210. For example, as illustrated in FIG. 2, connecting element 212 may be one or more hooks, affixed or integral to container 210, which allows 210 to be physically coupled to hangar bar 202. Further, connecting element 212 may facilitate the connection and disconnection of hangar bar and container 210.

Optional conductive element 208 may be used to electrically couple material 104 and hanger bar 202. Conductive element 208 may have any suitable cross-sectional geometry, such as, for example, round, hexagonal, square, rectangular, octagonal, oval, elliptical, or any other desired geometry. The desired cross-sectional geometry of the conductor elements may be chosen to optimize harvestability of copper and/or to optimize flow and/or mass transfer characteristics of the electrolyte within the electrowinning apparatus. Conductive element 208 may be configured in any manner now known or hereafter devised by the skilled artisan to provide a support and/or structure for high surface area material 104, to optimize harvestability of copper, and/or to optimize flow or mass transfer characteristics of the electrolyte within an electrowinning apparatus. In the illustrated example, cathode assembly 210 includes a plurality of conductive elements 208, in the form of conductive metal rods.

In accordance with alternate embodiments of the invention, conductive element 208 may be in the form of thin metal foil, having a thickness of about 0.02 to about 0.06 inches. A length of conductive element 208 may depend on a variety of factors. In accordance with exemplary embodiments of the invention, a length of conductive element 208 is between about a third of the active cathode area length to about an entire length of the cathode active area length. As used herein, “active area” of an electrode or the cathode assembly or an anode assembly refers to the surface area of the respective assembly that is immersed in the electrolyte during an electrowinning process. Similarly, a width of element 208 may depend on a variety of factors and may be configured to provide desired contact area with material 104.

FIG. 3 illustrates yet another exemplary cathode assembly 300 in accordance with additional exemplary embodiments of the invention, which includes a hanger bar 202, having curved ends 304, 306, a plurality of conductive elements 208, connecting elements 212, high surface area material 104, and a frame 310. Assembly 300 is similar to assembly 200, except assembly 300 includes a frame 310 in place of the flow-through container 210 of assembly 200.

Hanger bar 202, conductive elements 208, connecting elements 212, and high surface area material 104 may be the same or similar to those described above in connection with assemblies 100 and 200. Frame 310 may be configured to protect edges of material 104 and may be formed of any suitable material. By way of example, frame 310 is formed of a non-conductive material, such as polyethylene, polystyrene, polyvinyl chloride and/or polytetrafluoroethylene. Alternatively, frame 310 may be formed of conductive material, such as copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, combinations thereof, or other suitably conductive material. In accordance with further examples, frame 310 includes sides 316, 318, a bottom section (not illustrated) with holes for drainage, top sections 320, side sections 322, 324, and bottom sections 326. Top sections 320, side sections 322, 324, and bottom sections 326 are arranged about a perimeter of material 104, which allows electrolyte solution to flow through material 104, while frame 310 protects sides and edges of material 104.

FIG. 4 illustrates a portion of a system 400 for electrowinning metal from solution in accordance with exemplary embodiments of the invention. System 400 includes a cathode assembly 402, an anode assembly 404, a tank 406, and electrolyte solution 408. System 400 also includes power supplies coupled to the cathode assemblies and/or anode assemblies to provide a bias between cathode assembly 402 and anode assembly 404 sufficient to cause metal to deposit onto the active area of cathode assembly 402. Although illustrated with a single cell, including one cathode assembly 402 and one anode assembly 404, electrowinning systems in accordance with the present invention may include multiple cells, having anode assemblies and/or cathode assemblies coupled together in series and/or in parallel.

Anode assembly 404, tank 406, and electrolyte solution 408 may include any anode configuration, tank, an electrolyte used to recover metal from solution. Cathode assembly 402 includes high-surface area material (e.g., material 104) and may include any of the cathodes assemblies described herein. For example, system 400 may be configured for use in conventional electrowinning of metal (e.g., electrowinning of copper from solution including copper sulfate). Alternatively, system 400 may be configured for electrowinning metal (e.g., copper) powder from an electrolyte solution, using, for example, a ferrous/ferric anode reaction. Furthermore, as discussed in more detail below, system 400 may be portable, such that it can be assembled at or near a source of the metal to be recovered.

Anode assembly 404 may include a plate-type (i.e., non-flow-through) or a flow through active area. As used herein, “flow-through anode” refers to any anode that allows solution to flow through the active area of the anode—e.g., during the electrowinning process.

In the case when anode assembly 404 is a flow-through configuration, the active area of the anode may be configured as a porous metal sheet, metal wool, metal fabric, porous non-metallic materials, expanded porous metal, metal mesh (e.g., 80×80 strands per square inch or 30×30 strands per square inch), expanded metal mesh, corrugated metal mesh, a plurality of metal strips, multiple metal wires or rods, woven wire cloth, perforated metal sheets, the like, or combinations thereof. Anode assembly 404 may include a substantially planer or a three-dimensional surface.

The active surface of anode assembly 404 may include lead or a lead alloy, such as a lead-tin-calcium alloy, a valve metal, such as titanium, tantalum, zirconium, or niobium, other metals, such as nickel, stainless steel, or metal alloys, such as a nickel-chrome alloy, intermetallic mixtures, or a ceramic or cermet containing one or more valve metals. By way of example, the active surface includes titanium, which may be alloyed with nickel, cobalt, manganese, or copper to form the active surface.

The active area may also include any electrochemically active coating, including platinum, ruthenium, iridium, or other Group VIII metals, Group VIII metal oxides, or compounds comprising Group VIII metals, and oxides and compounds of titanium, molybdenum, tantalum, and/or mixtures and combinations thereof. Alternatively, the coating may include carbon, graphite, mixtures thereof, a precious metal oxide, a spinal-type material, a carbon composite, or a metal (e.g., titanium)-graphite sintered material.

Tank 406 is configured to retain solution 408 and to facilitate flow of solution 408 between and adjacent to cathode assembly 402 and anode assembly 404. In accordance with various embodiments of the invention, tank 406 includes a tapered bottom section to facilitate collection of electrowon metal powder.

As noted above, in accordance with various alternative exemplary embodiments, system 400 is a portable system and tank 406 is a portable tank. For example, system 400 may be configured so that it can be transported to and operated at areas with low grade supplies of metal (e.g., acid mine drainage, bleed streams and remediation streams) to be electrowon. In this case, tank 406 comprises a portable tank having a size of about 5 m³ to about 10 m³, formed of non-conductive materials, and cathode assemblies 402 and anode assemblies 404 are designed for portable applications. For example, cathode assemblies 402 and anode assemblies 404 may be reduced in size compared to larger, non-portable configurations. Further, multiple cathode assemblies 402 and anode assemblies 404 having active surface areas of from about 0.3 m³ to about 1.0 m³ (with one or two sides, for example) may be utilized with tank 406 with appropriate spacing to accommodate desired metal production rates.

Whether system 400 is stationary or portable, in accordance with various embodiments of the invention, system 400 is designed, such that cathode assembly 402 and anode assembly 404 are placed as close together as possible, without causing a direct electrical short between assemblies 402, 404. In cases where either assembly includes a non-conductive frame or container as described above in connection with exemplary assemblies illustrated in FIGS. 1 and 3, assemblies 402, 404 may be in direct contact, or may be spaced apart, for example having a spacing of less than about 2 inches, or about 0.25 inches to about 1.5 inches.

Electrolyte 408 may include any suitable solution including conductive ions to be recovered. By way of particular examples, system 400 may be used for direct electrowinning of copper metal from a pregnant leach solution (e.g., a solution that has not been treated with conventional concentrating or solvent extraction processes) or other sources of metal, such as low grade solutions. In the case of a pregnant leach solution, the PLS may be obtained from a leaching process (e.g., a heap leach, a vat leach, a tank leach, a pad leach, a leach vessel or any other leaching technology useful for leaching a metal value from processed metal-bearing material). In accordance with some exemplary embodiments of the invention, the leach solution may be conditioned using, for example, a solid-liquid phase separation step, an additional leach step, a pH adjustment step, a dilution step, a concentration step, a metal precipitation step, a filtering step, a settling step, as well as any combinations thereof.

In accordance with other examples, electrolyte 408 includes a solution recovered from previous physical or chemical processes. For example, electrolyte 408 may comprise a recycle (e.g., lean electrolyte) stream from another, previous electrowinning process. Electrolyte 408 may also comprise a bleed stream. Other sources for electrolyte 408 include acid mine drainage streams, remediation solution, and other polluted water supplies. However, any electrolyte 408 which contains a suitable amount of metal to be recovered by system 400 is in accordance with the present disclosure.

In accordance with particular embodiments of the invention, solution 408 includes a copper ion concentration of about 0.1 g/l to about 2.5 g/l copper ion. The electrolyte may also include about 1 to about 10 g/l acid.

In accordance with various embodiments of the invention, electrolyte 408 includes iron ions (ferrous and ferric iron ions) which are co-extracted with copper in the leaching step. In accordance with various aspects of these embodiments, solution 408 includes about 0.5 g/l to about 3.5 g/l total iron ion concentration. In accordance with additional aspects, the ferric ion concentration is about 0.1 g/l to about 1 WI.

To maintain desired operating efficiency, defined as the actual amount of metal plated divided by the theoretical amount of metal that could be plated for a set of conditions, electrolyte 408 includes a relatively high Cu/Fe³⁺ ratio (e.g., about 2 to about 6) and relatively high Fe²⁺/Fe³⁺ ratio (e.g., about 2 to about 8).

During the electrowinning process, described in more detail below, when electrolyte 408 includes iron ions, the ferrous ions may be oxidized to ferric ions at the anode, and thus the concentration of ferrous ions is depleted during the process, while the concentration of ferric ions is increased. An amount of ferrous ions in the electrolyte may be controlled by, for example, addition of ferrous sulfate to solution 408 and the amount of ferric ions can be controlled through, for example, solution extraction of the ferric ions. Ferrous/ferric ions can also be leached from ore or any iron source to generate additional iron, preferably in the form of ferrous ions. Additionally and/or alternatively, sulfur dioxide or other suitable reducing agent, alone or in the presence of a catalyst, may be added to electrolyte 408 (e.g., as part of a regeneration process) to reduce the ferric ion concentration to desired levels. In addition, the pH of solution 408 may be adjusted to reduce the ferric ion concentration to desired levels.

System 400 may also include electrolyte pumping, circulation, and/or agitation systems (not illustrated) to maintain desired flow and circulation of solution 408 between the active areas of cathode assembly 402 and anode assembly 404 and adjacent the active areas of the respective assemblies. In accordance with various embodiments of the invention, a solution flow rate is between about 0.05 m/ft² of active cathode area to about 5 m/ft² of active cathode area.

FIG. 5 illustrates a method 500 for recovering metal in accordance with further exemplary embodiments of the invention. Method 500 includes the steps of providing a solution including metal ions (step 502), optionally conditioning the solution (step 504), electrowinning metal using a high surface area cathode assembly (step 506), and harvesting the metal (step 508).

During step 502, an electrolyte solution suitable for electrowinning metal ions from the solution is provided. The solution may include any of the solutions described above in connection with solution 408 and may suitably be provided in a tank, such as tank 406.

If desired, the solution including metal ions may be conditioned during step 504. Conditioning step 504 may include, for example, filtration to remove particles from the solution. When the solution includes a pregnant leach solution, conditioning step 504 may additionally or alternatively include, for example, adding ferrous ions and/or removing ferric ions. This conditioning process may be used to manipulate (e.g., increase) an efficiency of an electrowinning system, such as system 400. For example, when system 400 is used for direct electrowinning of copper using a ferrous/ferric anode reaction, an efficiency of system 400 can be increased by increasing Cu/Fe³⁺ and Fe²⁺/Fe³⁺ ratios.

During step 506, metal is recovered from the solution, using, e.g. system 400, by applying a sufficient bias across a cathode assembly (e.g., assembly 402) and an anode assembly (e.g., assembly 404) to cause metal ions in solution (e.g., solution 408) to deposit onto an active area of the cathode assembly. Step 506 may be performed under constant current or constant voltage operating conditions. In accordance with exemplary embodiments of the invention, step 506 is performed using a constant voltage source with a voltage of about 1.0 V to about 2.5 V. In this case, exemplary current densities range from about 5 amp/ft² of apparent active cathode area to about 25 amp/ft² of apparent active cathode area.

Metal is recovered during step 508. In accordance with exemplary embodiments of the invention, metal is harvested in solid form. However, in accordance with alternative embodiments, the metal may be recovered in powder form.

In the case of powder recovery, while in situ harvesting techniques may be desirable to minimize movement of cathodes and to facilitate the removal of copper powder from an electrowinning system (e.g., system 400) on a continuous basis, any number of mechanisms may be utilized to harvest the metal (e.g., copper) powder product from the cathode in accordance with various aspects of the present disclosure. Any device now known or hereafter devised that functions to facilitate the release of copper powder from the surface of the cathode to, e.g., a base portion of the electrowinning apparatus, enabling collection and further processing of the copper powder may be used. The optimal harvesting method and apparatus for a particular embodiment will depend largely on a number of interrelated factors, primarily current density, copper concentration in the electrolyte, electrolyte flow rate, and electrolyte temperature. Other contributing factors include the level of mixing within the electrowinning apparatus, the frequency and duration of the harvesting method, and the presence and amount of any process additives (such as, for example, flocculant, surfactants, and the like).

In accordance with various embodiments of the invention, in situ harvesting, using either self-harvesting (described below) or other in situ devices are used for the removal of copper powder from the electrowinning cell. Examples of harvesting techniques for use with various embodiments include vibration (e.g., one or more vibration and/or impact devices affixed to one or more cathodes to displace copper powder from the cathode surface at predetermined time intervals), a pulse flow system (e.g., electrolyte flow rate increased dramatically for a short time to displace copper powder from the cathode surface), use of a pulsed power supply to the cell, use of ultrasonic waves, and use of other mechanical displacement means to remove copper powder from the cathode surface, such as intermittent or continuous air bubbles. Alternatively, “self-harvest” or “dynamic harvest” may be my employed when the electrolyte flow rate is sufficient to displace copper powder from the cathode surface as it is formed or shortly after deposition and crystal growth occurs. As noted above, surface finishes (e.g., polishing) may be advantageously employed to enhance harvestability. The copper powder that is carried through the cell with the electrolyte may be removed via a suitable filtration, sedimentation, or other fines removal/recovery system.

As noted above, in accordance with some embodiments of the invention, metal is recovered from solution, e.g., a low-grade solution at a remote site using a portable electrowinning system (e.g., system 400). In this case a method for recovering metal may additionally include the steps of selecting a site at or near the source of the metal, placing a portable electrowinning system on the site, and operating the system at the site.

Although this disclosure has been described above with reference to a number of exemplary embodiments, it should be appreciated that the particular embodiments shown and described herein are illustrative of the invention and its best mode and are not intended to limit in any way the scope as set forth in the claims. Those skilled in the art having read this disclosure will recognize that changes and modifications may be made to the exemplary embodiments without departing from the scope thereof. For example, various aspects and embodiments may be applied to electrolytic recovery of metals other than copper, such as nickel, zinc, cobalt, and others. Although certain preferred aspects are described herein in terms of exemplary embodiments, such aspects may be achieved through any number of suitable means now known or hereafter devised. Accordingly, these and other changes or modifications are intended to be included within the scope of the present disclosure. 

What is claimed is:
 1. A high surface area cathode assembly for electrowinning metal from solution, the cathode assembly comprising: a hanger bar; a high surface area material in contact with the hanger bar, the high surface area material having a surface area to volume ratio of about 0.05 ft²/in³ to about 10 ft²/in³; and a container about at least a portion of the high surface area material.
 2. The high surface area cathode assembly of claim 1, wherein the high surface area material comprises material selected from the group consisting of metal hair wire, metal wool, metal fabric, metal foam, and conductive polymers.
 3. The high surface area cathode assembly of claim 2, wherein the high surface area material comprises at least one of a copper mesh, a copper wool, a copper fabric, a copper foam, and a copper hair wire.
 4. The high surface area cathode assembly of claim 1, wherein the surface area to volume ratio is about 0.1 ft²/in³ to about 5 ft²/in³.
 5. The high surface area cathode assembly of claim 1, wherein the hanger bar comprises material selected from the group consisting of copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, and combinations thereof.
 6. The high surface area cathode assembly of claim 1, wherein the container comprises a material selected from the group consisting of polyethylene, polystyrene, polyvinyl chloride, and polytetrafluoroethylene.
 7. The high surface area cathode assembly of claim 1, wherein the container is a flow-through container comprising a plurality of voids and an open area of about 20% to about 80%.
 8. The high surface area cathode assembly of claim 1, further comprising a connecting element coupled to the container and the hanger bar.
 9. The high surface area cathode assembly of claim 1, further comprising a conductive element.
 10. The high surface area cathode assembly of claim 9, wherein the conductive element comprises at least one conductive rod.
 11. The high surface area cathode assembly of claim 9, wherein the conductive element comprises a metal sheet.
 12. The high surface area cathode assembly of claim 9, wherein the conductive element comprises material selected from the group consisting of copper, copper alloy, copper aluminum alloys, aluminum, stainless steel, titanium, gold, and combinations thereof.
 13. A system for electrolytic recovery of metal, the system comprising: an anode assembly; a high surface area cathode assembly comprising a hanger bar, a high surface area material, the high surface area material having a surface area to volume ratio of about 0.05 ft²/in³ to about 10 ft²/in³, and a container about at least a portion of the high surface area material; and an electrolyte solution between the anode assembly and the cathode assembly; and a tank containing the electrolyte solution.
 14. The system for electrolytic recovery of metal of claim 13, wherein the electrolyte solution comprises pregnant leach solution.
 15. The system for electrolytic recovery of metal of claim 13, wherein the electrolyte solution further comprises iron ions.
 16. The system for electrolytic recovery of metal of claim 13, wherein the system is a portable system and is placed near a source of the electrolyte solution.
 17. The system for electrolytic recovery of metal of claim 13, wherein a portion of the anode assembly and a portion of the cathode assembly are in direct contact.
 18. The system for electrolytic recovery of metal of claim 13, wherein the cathode assembly further comprises a conductor element coupled to the hanger bar.
 19. The system for electrolytic recovery of metal of claim 13, wherein the electrolyte solution comprises a Cu/Fe³⁺ ratio of about 2 to about
 6. 20. The system for electrolytic recovery of metal of claim 13, wherein the electrolyte solution comprises a Fe²⁺/Fe³⁺ ratio of about 2 to about
 8. 21. The system for electrolytic recovery of metal of claim 13, wherein the high surface area material comprises at least one of a copper mesh, a copper wool, a copper fabric, a copper foam, and a copper hair wire.
 22. The system for electrolytic recovery of metal of claim 13, wherein the cathode assembly further comprises a connecting element coupled to the hanger bar and the container.
 23. The system for electrolytic recovery of metal of claim 13, wherein metal ions are recovered from the electrolyte solution in the form of metal powder.
 24. The system for electrolytic recovery of metal of claim 23, wherein the metal powder is self-harvested from the cathode assembly.
 25. A method of recovering metal from an electrolyte solution, the method comprising the steps of: providing an electrolyte solution; electrowinning metal from the electrolyte solution using a high surface area cathode assembly having high surface area material with a surface area to volume ratio of about 0.05 ft²/in³ to about 10 ft²/in³; and harvesting the metal in the form of metal powder.
 26. The method of recovering metal from an electrolyte solution of claim 25, wherein the step of electrowinning is performed at a constant voltage.
 27. The method of recovering metal from an electrolyte solution of claim 25, wherein the electrolyte solution comprises one of a recycled solution, bleed solution, remediation solution, waste water solution, or acid mine drainage stream.
 28. The method of recovering metal from an electrolyte solution of claim 25, wherein the electrolyte solution contains between 0.1 g/l and 2.5 g/l of metal ions.
 29. The method of recovering metal from an electrolyte solution of claim 25, wherein the step of harvesting the metal in the form of metal powder comprises one of self-harvesting or dynamic harvesting. 